The present invention relates generally to the field of human genetics. Specifically, the present invention relates to methods and materials used to detect a human sporadic dilated cardiomyopathy (DCM) gene, specifically the dystrophin gene, some mutant alleles of which cause susceptibility to sporadic DCM. More specifically, the invention relates to germline mutations in the dystrophin gene and their use in the diagnosis of predisposition to sporadic DCM. The invention also relates to the prophylaxis and/or therapy of sporadic DCM associated with a mutation in the dystrophin gene. The invention further relates to the screening of drugs for sporadic DCM therapy. Finally, the invention relates to the screening of the dystrophin gene for mutations/alterations, which are useful for diagnosing the predisposition to sporadic DCM.
The publications and other materials used herein to illuminate the background of the invention, and in particular, cases to provide additional details respecting the practice, are incorporated herein by reference, and for convenience, are referenced by author and date in the following text and respectively grouped in the appended Bibliography.
The dilated cardiomyopathies are a heterogeneous group of disorders with different inheritance patterns, including autosomal dominant (˜23%), X-linked (˜5%), autosomal recessive, and mitochondrial transmission (Bowles et al., 2000). Approximately 30% of all DCM is thought to be inherited, while 70% is sporadic (Bowles et al., 2000). It has been speculated that a high percentage of the sporadic cases are due to acquired disease, including myocarditis or coronary artery disease, but little specific supporting data for these etiologies are available.
DCM is common in patients with Duchenne Muscular Dystrophy (DMD), but it most frequently occurs late in the disease and it is a terminal event in about 10% of patients with DMD (Hunsaker et al., 1982; Perloff et al. 1966). In patients with Becker muscular dystrophy (BMD), cardiomyopathy can be an earlier and prominent feature. Some patients with identical mutations in the dystrophin gene may develop DCM while some do not. However, there is no good genotype to phenotype correlation in patients with DMD or BMD (Muntoni et al., 1993; Beggs et al., 1991; Gold et al., 1992). Variants of the dystrophin gene have been associated with X-linked DCM. The reports fall into two classes: i) mutations in the promoter region or exon 1 of the muscle transcript (Muntoni et al., 1993; Yoshida et al., 1998; Muntoni et al., 1995a; Muntoni et al., 1995b; Milasin et al., 1996) and, ii) mutations elsewhere in the gene (Ortiz-Lopez et al., 1997; Ferlini et al., 1998; Muntoni et al., 1997). The mutations within the promoter region and exon 1 of the major muscle transcript are associated with up-regulation of alternative dystrophin transcripts and the presence of brain and Purkinje cell dystrophin isoforms in skeletal muscle (Muntoni et al., 1995b). However, no dystrophin transcripts and protein are found in cardiac muscle in these patients.
Four mutations elsewhere in the gene have been described. An Alu-like sequence rearrangement has been found 2.4 kb into intron 11, resulting in activation of a cryptic splice site and producing an alternative transcript with numerous in frame stop codons (Ferlini et al., 1998). Only the mutant mRNA was detected in heart muscle, but some normal transcript also was found in skeletal muscle. Two deletions in the deletion hot spot region normally associated with BMD were described in two patients with dilated cardiomyopathy (Muntoni et al., 1997). Arbustini et al. (2000) found that four of 201 adult male patients (2%) with cardiomyopathy had deletions previously described in patients with BMD (Muntoni et al., 1993; Beggs et al., 1991; Gold et al., 1992) who did not have a previous diagnosis of muscular dystrophy. The reason that these patients did not have BMD is unclear. Finally a missense mutation was described in exon 9 (Ortiz-Lopez et al., 1997). The mutation was in an amino acid that is only moderately conserved (identical in mouse, dog and chicken, but not conserved in Drosophila dystrophin and in three utrophins). The significance of this one missense mutation is unknown since polymorphic missense mutations are common in the dystrophin gene (Mendell et al., 2001).
In view of the importance of early diagnosis of sporadic DCM, it is desired to identify genes associated with sporadic DCM for diagnostic and therapeutic purposes.